1. Field of the Invention
This invention relates to an optical waveguide apparatus which controls signal light traveling through an optical waveguide by means of other light.
2. Description of the Related Art
In recent years, various optical integrated circuits using optical waveguides have been proposed (e.g., "OPTICS LETTERS Vol. 15 No. 1 Jan. 1, 1990. A grating element is one of elements used in an optical integrated circuit. Of grating elements, passive grating elements and functional grading elements are known. A passive grating element is incorporated in an optical waveguide, and a functional grating element is formed by utilizing an electro-optical effect, electromagnetic effect, thermal optical effect, acoustooptical effect, and the like of the material of which an optical waveguide is made. The functional grating serves as an deflector, a reflector, a wavelength filter, a connector, and a mode converter, with respect to guided light, since it has a fine cyclic structure in the order of light wavelength. The function of the passive grating is fixed, while that of the functional grating is controlled by an electrical signal, or the like.
An optical switch is known as a functional grating utilizing a photorefractive effect. FIGS. 9 (A) to (C) schematically show the functional grating, in which optical waveguides 2 and 3 are formed in a substrate 1, crossing each other. A donor-type impurity is introduced into a crossing portion 4 uniformly to generate a photorefractive effect in the portion, thereby forming an optical waveguide apparatus. As shown in FIG. 9 (A), if control light (light flux) 5a or 5b is not applied to the apparatus, a waveguide signal 6 is transmitted through the optical waveguide 2. If two coherent fluxes 5a and 5b having relatively short wavelengths and energy higher than a difference .DELTA.E between the energy level of the donor of the crossing portion 4 and the energy level at an end of the conductive band are spatially introduced and interfere with each other in the crossing portion 4 as indicated by arrows shown in FIG. 9 (B), a grating of refractive index distribution type is generated in the portion 4 by the photorefractive effect. Further, as is shown in FIG. 9 (C), the signal light 6 transmitted through the optical waveguide 2 is diffracted by the grating generated in the crossing portion 4 by suitably changing the pitch and the direction of interference fringes formed by the applied light, and changed into a signal light 7 transmitted through the optical waveguide 3. In this way, optical switching is performed.
FIG. 10 shows an optical switch array. In the array, a plurality of optical switches shown in FIG. 5 are arranged in a matrix, and a light valve array 8 formed of liquid crystal or the like is formed on the switches. With this structure, interference light is selectively introduced into the optical switch array to operate a desired optical switch. In FIG. 10, reference numerals 6a, 6b, and 6c denote input signal light, and 7a, 7b, and 7c output signal light.
The above-mentioned passive grating performs only a specific function and cannot control guided light actively, since a cyclic structure having a diffraction function is incorporated in the optical waveguide.
In general, the functional grating actively controls guided light by means of an electrical signal supplied to an electrode formed on the optical waveguide substrate. However, if light modulated by another optical waveguide apparatus or the like is used as a control signal, or if light spatially-modulated is used as a control signal, a light signal applied to a control section must be converted to an electrical signal or the like. In addition, it is difficult to spatially introduce an electrical signal into an optical waveguide substrate.
In the optical waveguide apparatus having the above-described functional grating utilizing photo-refractive effect, if vibration is applied while interference fringes are being formed, and the interference fringes or the optical waveguide apparatus itself moves, the refractive index modulation of the grating is adversely affected, and an expected operation is not obtained. To avoid this, it is necessary to form interference fringes which are not affected by vibration or the like, resulting in an complicated structure.